Methods, base station system, radio unit and radio head of a wireless communication network, for increasing signal quality of signals sent from the radio head to the radio unit

ABSTRACT

Disclosed is a method performed by a base station system of a wireless communication network, for increasing signal quality of signals sent from a radio head (RH) to a radio unit (RU) over a metallic conductor. The base station system comprising a baseband unit (BBU), the RU and the RH and the RU is connected to the RH via the metallic conductor. The method comprises, at the RH: amplifying, by an amplification unit, a signal to be transmitted from the RH to the RU; changing the signal amplification level of the amplification unit; and transmitting the amplified signal to the RU. The method further comprises, at the RU: receiving the amplified signal and compensating, by a compensating unit capable of adapting its amplification level, for the change in signal amplification level performed at the RH such that the strength of the signal is transparent to the base station system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/232,883, filed Aug. 8, 2014, which is the National Stage ofInternational Application No. PCT/EP2013/072490, filed Oct. 28, 2013,which claims priority to U.S. Provisional Patent Application No.61/882,390, filed Sep. 25, 2013, which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure relates generally to a method performed by a basestation system of a wireless communication network, for increasingsignal quality of signals sent from a radio head to a radio unit over ametallic conductor, wherein the base station system comprises a basebandunit, the radio unit and the radio head. The present disclosure furtherrelates to a corresponding base station system, a method performed by aradio unit, a radio unit, a method performed by a radio head and a radiohead.

BACKGROUND

Wireless communication networks have evolved from pure voice networks tohigh-speed data networks. The 4th generation radio network long-termevolution, LTE, is able to provide capacities exceeding 100 Mbit/s in anultra-dense small-cell installation. As most of the traffic in thewireless communication networks will be generated in-doors, ultra-densesmall-cell indoor network solutions are required. Different approacheshave been taken to provide network architectures able tocost-efficiently and reliably meet the run on high mobile capacity.

One such approach is to re-use existing metallic conductors inbuildings, such as copper cables, e.g. Ethernet cables, and to employ adistributed base station system comprising a base band unit, BBU, and aplurality of radio heads, RH. The RHs may also be called active antennaelements, AAEs. The BBU would communicate with the plurality of RHs viathe metallic conductors; one metallic conductor may be connected to oneRH. Such a system may be called a Radio over Copper, RoCU, system.

A problem in such a system is that in uplink (from the RH to the BBU);the signal sent through the metallic conductor may be disturbed due tonoise.

SUMMARY

It is an object of the invention to address at least some of theproblems and issues outlined above. It is an object to increase qualityof signals communicated uplink in a Radio over Copper, RoCU, system. Itis an object to reduce the noise factor of the RoCU system in uplink.

It is possible to achieve at least some of these objects by usingmethods, a RoCU system, a radio head and a radio unit as defined in theattached independent claims.

According to a first aspect, a method is provided performed by a basestation system of a wireless communication network, for increasingsignal quality of signals sent from a radio head, RH, to a radio unit,RU over a metallic conductor. The base station system comprising abaseband unit, BBU, the RU and the RH, wherein the RU is connected tothe RH via the metallic conductor. The method comprises, at the RHamplifying 102, by an amplification unit, a signal to be transmittedfrom the RH to the RU, changing 104 the signal amplification level ofthe amplification unit; and transmitting 108 the amplified signal to theRU. The method further comprises, at the RU receiving 114 the amplifiedsignal, compensating (116), by a compensating unit capable of adaptingits amplification level, for the change in signal amplification levelperformed at the RH such that the strength of the signal is transparentto the base station system.

According to a second aspect, a method is provided performed by a radiohead, RH, operable in a base station system of a wireless communicationnetwork, for increasing signal quality of signals transmitted from theRH to a radio unit, RU, over a metallic conductor, wherein the basestation system comprises a baseband unit, BBU, the RU and the RH, the RHbeing connected to the RU via the metallic conductor. The methodcomprises amplifying, by an amplification unit, a signal to betransmitted from the RH to the RU, changing the signal amplificationlevel and transmitting the amplified signal to the RU for subsequentcompensation for the signal amplification level change at the RH suchthat the strength of the signal is transparent to the base stationsystem.

According to a third aspect, a method is provided performed by a radiounit, RU, operable in a base station system of a wireless communicationnetwork, for increasing signal quality of signals sent from a radiohead, RH, to the RU over a metallic conductor. The base station systemcomprises a baseband unit, BBU, the RU and the RH, and the RU isconnected to the RH via the metallic conductor. The method comprisesreceiving a signal transmitted from the RH, the signal being amplifiedby an amplification unit at the RH and compensating, by a compensatingunit capable of adapting its amplification level, at the RU, for asignal amplification change performed at the RH such that the strengthof the signal is transparent to the base station system.

According to a fourth aspect, a base station system of a wirelesscommunication network is provided, the base station system comprising abaseband unit, BBU, a radio unit, RU and a radio head, RH. The RU isconnected to the RH via a metallic conductor and the BBU is connected tothe RU. The base station system is arranged for increasing signalquality of signals sent from the RH to the RU over the metallicconductor. The RH comprises an amplifying unit for amplifying a signalto be transmitted from the RH to the RU and for changing itsamplification level, and a transmitting unit for transmitting theamplified signal to the RU. The RU comprises a receiving unit forreceiving the amplified signal, and a compensating unit capable ofadapting its amplification level, for compensating for the change insignal amplification level performed at the RH such that the strength ofthe signal is transparent to the base station system.

According to a fifth aspect, a radio head, RH, operable in a basestation system of a wireless communication network, for increasingsignal quality of signals transmitted from the RH to a radio unit, RU,over a metallic conductor. The base station system comprises a basebandunit, BBU, the RU and the RH, the RH being connected to the RU via themetallic conductor. The RH comprises an amplifying unit for amplifying asignal to be transmitted from the RH to the RU and for changing theamplification level and a transmitting unit for transmitting theamplified signal to the RU for subsequent compensation for the signalamplification level change at the RH such that the strength of thesignal is transparent to the base station system.

According to a sixth aspect, a radio unit, RU, operable in a basestation system of a wireless communication network, arranged forincreasing signal quality of signals sent from a radio head, RH, to theRU over a metallic conductor. The base station system comprises abaseband unit, BBU, the RU and the RH, wherein the RU is connected tothe RH via the metallic conductor. The RU comprises a receiving unit forreceiving a signal transmitted from the RH, the signal being amplifiedat the RH and a compensating unit capable of adapting its amplificationlevel for compensating for the signal amplification performed at the RHsuch that the strength of the signal is transparent to the base stationsystem.

According to other aspects, computer programs and computer programproducts for being run on an RH or an RU are provided.

The above methods, RoCU system, radio head, radio unit, computer programproducts and computer programs may be configured and implementedaccording to different optional embodiments. Further possible featuresand benefits of this solution will become apparent from the detaileddescription below.

BRIEF DESCRIPTION OF DRAWINGS

The solution will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of a RoCU system according to anembodiment.

FIG. 2 is a schematic view of an exemplary cellular communicationnetwork to which coverage is provided by the RoCU system.

FIGS. 3-7 are flow charts of methods according to exemplary embodiments.

FIG. 8 is a schematic block diagram of an embodiment of a base stationsystem.

FIGS. 9-10 are flow charts showing noise figures of differentembodiments.

FIGS. 11-14 are schematic block diagrams of embodiments of base stationsystems.

FIG. 15 is a flow chart showing noise figures of an embodiment.

FIG. 16 is a schematic block diagram of an exemplary embodiment of abase station system comprising an RU and an RH.

FIG. 17 is a schematic block diagram of an exemplary embodiment of anRH.

FIG. 18 is a schematic block diagram of an exemplary embodiment of anarrangement in an RH.

FIG. 19 is a schematic block diagram of an exemplary embodiment of anRU.

FIG. 20 is a schematic block diagram of an exemplary embodiment of anarrangement in an RU.

DETAILED DESCRIPTION

Briefly described, a solution is provided for reducing the noise factorof a RoCU system in uplink. This is achieved by a first amplifieramplifying the signal at the RH side, before the signal is transmittedover the metallic conductor and then at the RU side, using a secondamplifier for compensating for changes in the amplification level at theRH side such that the signal strength is transparent to the base stationsystem. More particularly, the second amplifier compensates for anamplification change of +X dB at the first amplifier by changing itsamplification level by −X dB. Note that X may be a positive or anegative number, wherein a negative number means attenuation. Thereby itis possible to keep a high amplification level at the RH side for lowand normal input signal levels, but to lower the amplification level forhigh input signal levels. As a result, the noise factor of the systemwill be low for the desired signal level in a normal scenario, while thesystem is protected from the strong input signal in a blocking scenario.Low noise factor means that the noise introduced by the receiver is low.Low noise factor means high receive sensitivity, by which the receivercan decode weak signals. Noise factor is normally in linear scale, whilenoise factor in dB is usually referred to as noise figure. At the sametime, since this system makes it possible to lower the amplificationlevel for high input levels, it is avoided to exceed the allowed maximumsignal level for the metallic conductors for high input levels.

FIG. 1 shows an architecture of a base station system 100, also called aRoCU system, according to an embodiment of the invention for connectingantennas to a BBU 30 over metallic conductors 40, e.g. copper cablessuch as Cat 5/6/7 cables. The base station system 100 comprises the BBU30 which is arranged to treat signals in a baseband frequency region,typically in a low frequency region. The base station system 100 furthercomprises a radio unit, RU, 10 connected to the BBU 30 via e.g. anoptical fiber 32. Alternatively, for example: when RU and BBU areclosely located, the connection between the RU and the BBU may beelectrical via e.g. copper cables. The BBU 30 is arranged to generateand send a number of downlink baseband signals, also called IQ dataflows, to the RU, which IQ data flows are directed to radio heads 21-26.The number of downlink baseband signals may be sent as a single digitalsignal from the BBU to the RU, over the optical fiber, e.g. using CommonPublic Radio Interface, CPRI. The radio unit, RU, 10 is arranged forgenerating downlink, DL, radio signals in a low intermediate frequency,IF, band from the downlink baseband signals received from the basebandunit 30. The base station system 100 further comprises a number ofremote radio heads, RH, 21-26 connected to the RU 10 via the metallicconductors 40. Each RH is connected with a dedicated metallic conductorback to the RU. The radio unit 10 is further arranged to send the DL IFradio signals to the RHs via the metallic conductors. By transmitting IFsignals instead of high frequency RF signals over the metallicconductors, the cable loss is reduced. An RH 21-26 is arranged forpicking up the analog IF radio signals from the metallic conductor towhich it is connected and for converting the IF signals to the actualradio frequency, RF, to be transmitted over the air from antenna(s) ofthe RH. A radio frequency region may be e.g. 400 MHz to 6 GHz. The RHcomprises at least one antenna element for transmitting the DL signal toUEs.

In the uplink direction, the RHs 21-26 are each arranged to receive RFradio signals from user equipments, e.g. mobile stations, mix the RFsignals to IF signals to be transported over the metallic conductorstowards the RU 10 for further processing. The RU is arranged todown-convert the received IF signal to a baseband frequency for furthertransmission to the BBU 30. Uplink and downlink IF signals may betransported over the metallic conductors 40 via frequency duplexing forFDD radios, and/or time duplexing for TDD radios. A RoCU system is acost-effective radio system, especially for indoor deployment.

FIG. 2 shows a schematic view of an example of how the RHs 21-26 of FIG.1 may be positioned to cover a geographical area. Each RH 21-26 covers ageographical area 51-56. A mobile station 60 that is situated in e.g.geographical area 54 will be connected to RH 24 and receive DL RFsignals over the air from RH 24 and transmit UL RF signals over the airto RH 24. Even though FIG. 2 shows circular geographical areas, socalled omnicells, any other type of geographical area may be covered,such as an angular section, a part of a building floor etc. The RHs maybe arranged in a building, e.g. on different floors of the building.

FIG. 3 describes a method according to an embodiment performed by a basestation system 100 of a wireless communication network, for increasingsignal quality of signals sent from an RH 21 to an RU 10 over a metallicconductor 40. The base station system comprises a BBU 30, the RU 10 andthe RH 21. The RU 10 is connected to the RH 21 via the metallicconductor 40. The method comprises, at the RH, amplifying 102, by anamplification unit, a signal to be transmitted from the RH to the RU,changing 104 the signal amplification level of the amplification unit,and transmitting 108 the amplified signal to the RU. The method furthercomprises, at the RU, receiving 114 the amplified signal, andcompensating 116, by a compensating unit capable of adapting itsamplification level, for the change in signal amplification levelperformed at the RH such that the strength of the signal is transparentto the base station system.

The amplified signal is transmitted to the RU over time (preferablycontinuously) such that it is transmitted before and after the change ofsignal amplification level. To compensate for a change in signalamplification level performed at the RH such that the strength of thesignal is transparent to the base station system signifies that when thesignal amplification at the RH is increased with an amount, a signalamplification at the RU is decreased with approximately the same amountin the compensating step. For example, if the amplification level at theRH side is increased with 3 dB, the amplification level at the RU sideis decreased with approximately 3 dB. Similarly, if the amplificationlevel at the RH side is decreased with 5 dB, the amplification level atthe RU side is increased with 5 dB. The strength of the signal may alsobe called signal power. That the strength of the signal is transparentto the base station system signifies that the signal power istransparent from the antenna of the RH to the input of an analogue todigital converter, ADC, of the RU (see e.g. FIG. 8).

As a further example, the amplification unit at the RH side has a normalsetting level of 40 dB, further assuming cable loss 30 dB, and thecompensating unit at the RU side has a normal setting level of 0 dB,resulting in a total amplification of 10 dB to the UL signal. Then theamplification level at the RH side is decreased with 5 dB, due to e.g.an increase in signal input level which would result in a signal levelabove what is allowed over the metallic conductor if the signal isamplified with 40 dB at the RH side. To compensate for thisamplification decrease at the RH side, the amplification level at the RUside is increased with 5 dB. As a result, the total amplification fromthe antenna of the RH to the input of the ADC of the RU is still 10 dB,i.e. the signal strength is transparent to the base station system.

By such a method, a signal incoming to the RH may be amplified to a highsignal level while the gain of the whole receiver chain remains fixedwithout risking exceeding the signal level being above what is allowedover the metallic conductor and/or overdriving the electronic componentsin the chain, e.g. mixers, amplifiers etc, and creating imbalanced gainsor link budgets in UL and DL. As a result, the noise figure of thecommunication system (i.e. RoCU system) is significantly reduced.Thereby, longer metallic conductors can be used. Also, the radiocoverage is increased since weaker signals can be received at theantenna of the RH, amplified and transmitted over the metallicconductor.

Further, noise figure of the RoCu system is reduced in uplink (UL) andtherefore the UL dynamic range is increased. Further, cable reach andradio coverage is increased in the RoCu system.

According to an embodiment, the method of FIG. 3 may further comprise,at the RH, transmitting 106 information of a current signalamplification level at the RH to the RU, and, at the RU, receiving 112information of the current amplification level at the RH. Thecompensation 116 is then performed according to the receivedinformation. The information of a current amplification level may be forexample the actual amplification level used at the amplification unit ofthe RH, e.g. 40 dB, or information of amplification change since lasttime, e.g. a change of +5 dB. It may also be information ofamplification decrease or increase, for example in a stepwise manner,e.g. amplification has increased with an increment, or decreased with anincrement. A large amplification change at the RH side would then resultin a number of information signals being sent to the RU, e.g. if theincrement is set to 1 dB, a change of 5 dB at the RH side would resultin 5 information signals being sent, each informing of an increase inamplification level at the RH side. Thereby, the RU is informed how toadjust the amplification of its compensating unit such that strength ofthe signal is transparent to the base station system.

FIG. 4 (and FIG. 1) describes a method according to an embodimentperformed by a radio head, RH 21, operable in a base station system 100of a wireless communication network, for increasing signal quality ofsignals transmitted from the RH to a radio unit, RU 10, over a metallicconductor 40. The base station system comprises a baseband unit, BBU 30,the RU and the RH, the RH being connected to the RU via the metallicconductor. The method comprises amplifying 202, by an amplificationunit, a signal to be transmitted from the RH to the RU. The methodfurther comprises changing 206 the signal amplification level; andtransmitting 210 the amplified signal to the RU for subsequentcompensation for the signal amplification level change at the RH suchthat the strength of the signal is transparent to the base stationsystem.

According to an embodiment, the signal to be transmitted is amplified202 to a signal strength level approximately equal to a maximum allowedsignal strength level of the metallic conductor, or is amplified 202 bya maximum possible gain of the amplifier, when the signal strength levelto which the signal is amplified with maximum possible gain is below themaximum allowed signal strength level of the metallic conductor.Thereby, a high signal to noise ratio is achieved over the metallicconductor, which results in a low noise figure.

According to another embodiment, the method may further comprisetransmitting 208 information of a current signal amplification level tothe RU. The signal amplification level means how much the signal isamplified at the RH. The signal may be amplified by an amplificationunit, and the amplification may be determined as output level at anoutput of the amplification unit divided by an input level at an inputof the amplification unit. The amplification unit may be an AGC. Bytransmitting information of the current signal amplification level tothe RU it is possible for the RU to determine how much the signalamplification level has changed at the RH and thereby how to adapt thegain amplification of its compensating unit.

According to another embodiment, the information of the signalamplification level is transmitted 208 over a carrier frequency outsidea frequency band used for the transmission of the amplified signal.Thereby, a more robust communication channel can be selected for theinformation of the current amplification level than used for the actualsignal, which ensures that the information is correctly received at theRU-side.

According to another embodiment, shown in FIG. 5, the method furthercomprises delaying 207 the transmission of the amplified signal to theRU in relation to the transmission 208 of the information of the currentamplification level such that the signal is received at the RU atsubstantially the same time as a compensation is started to be performedat the RH according to the transmitted information of the currentamplification level. The transmission of the information ofamplification level may have some processing delay in relation to thetransmission of the actual signal, which results in that the informationof a gain change is received later than the actual signal at the RU. Asa result, the compensation is performed a bit too late. This delay maycause glitches in the signals. This embodiment makes it possible toconsiderably shorten such glitches. The processing delay may occur dueto modulation and/or encoding of the information at the RH before it istransmitted, and a corresponding demodulation and decoding at theRU-side, when received. In an alternative embodiment, the delay of thesignal may instead be performed at the RU side, before the signal is fedto the compensating unit.

FIG. 6 (and FIG. 1) describes a method according to an embodimentperformed by a radio unit, RU, 10 operable in a base station system 100of a wireless communication network, for increasing signal quality ofsignals sent from a radio head, RH 21, to the RU 10 over a metallicconductor 40. The base station system 100 comprises a baseband unit, BBU30, the RU and the RH. The RU is connected to the RH via the metallicconductor. The method comprises receiving 306 a signal transmitted fromthe RH, the signal being amplified by an amplification unit at the RH,and compensating 308, by a compensating unit capable of adapting itsgain amplification, at the RU, for a signal amplification changeperformed at the RH such that the strength of the signal is transparentto the base station system.

According to an embodiment, the method of FIG. 6 may also comprisereceiving 302 information of a current amplification level at the RHfrom the RH, and controlling the compensation of the compensating unitaccording to the received information.

If the information of the current amplification level at the RH showsthat the amplification level has decreased with a certain amount sincelast received information, the compensating in the RU is performed suchthat the amplification level of the compensating unit is increased withthe same amount. According to an embodiment, this may be accomplished byusing a look-up table. The gain settings of the amplification unit andthe compensating unit are then 1-to-1 mapped such that the compensatingunit compensates the amplification unit gain changes accordingly. Thecompensating unit just needs to use the corresponding gain value in thetable once the compensating unit gain setting is known. In this way, theRU knows how to adjust the amplification of its compensating unit suchthat strength of the signal is transparent.

According to another embodiment, the receiving 302 of information maycomprise, at a first point of time, receiving information from the RH ofa current amplification level at the RH and at a second point of timelater than the first point of time, receiving information from the RH ofa current amplification level at the RH, and comparing the amplificationlevel at the second point of time with the amplification level at thefirst point of time to detect a difference in amplification level. Thenthe compensating 308 may be controlled according to the detecteddifference in amplification level.

According to another embodiment, the information of the currentamplification level may be received 302 over a carrier frequency outsidea frequency band used for the reception of the signal. “A carrierfrequency” signifies one or more carrier frequencies. The informationmay be transmitted over one frequency or over more than one carrierfrequency.

According to another embodiment, shown in FIG. 7, the method may furthercomprise, after the compensation 308 has been performed, detecting 310sudden changes in signal strength, and adjusting 312 the detectedchanges such that the signal strength is reduced at the detectedchanges. Thereby, glitches in the signal strength are compensated for,e.g. smoothed out.

According to another embodiment, the information of the currentamplification level may be modulated and possibly also encoded by the RHbefore the information is transmitted to the RU. Further, the receivedinformation of the current amplification level may then be demodulatedand possibly also decoded by the RU.

According to another embodiment, the compensating for a signalamplification adjustment performed at the RH is only performed if undernormal operating conditions, and, if under a special operating conditiondiffering from the normal operating conditions, the compensating for thesignal amplification adjustment performed at the RH is only partiallyperformed, i.e. the change of amplification level is only partiallycompensated. The term “under normal operating conditions” may mean whenthe signal strength of the received signal is below a signal strengththreshold, the signal strength threshold representing a signal of ablocking user, which signal results in a noise figure increase above acertain level. A special operating condition may mean when the signalstrength of the received signal is above the same signal strengththreshold. This embodiment is especially advantageous in a distributedantenna system, DAS, configuration. For more information of a DAS, seeFIG. 14. In a DAS, employing such an embodiment in one branch (i.e.subsystem comprising an RH connected to an RU), reduces noise figure forother branches in the DAS, and therefore benefits other users connectedto other branches, even though the partially compensated branch ispenalized a bit. But the partially compensated branch anyway has adegraded performance due to deep blocking (strong blocking signal).

According to an embodiment, the RH comprises an AGC (automatic gaincontrol) and the RU comprises a gain compensator (e.g. a VGA, variablegain amplifier or a variable attenuator), both arranged in the ULdirection. The gain compensator may be arranged to simultaneouslycompensate for the gain adjustment performed by the AGC. For example, ifthe AGC increases the gain by 3 dB, the gain compensator reduces itsgain by 3 dB such that the signal strength is transparent to the BBU.According to an embodiment, the AGC amplifies the UL received signal toa maximum transmit signal strength allowed at the copper interface oramplifies the UL received signal with the maximum gain such that thetransmit signal strength is less than the maximum allowed signalstrength at the metallic conductor interface, e.g. copper cable.According to another embodiment, information of the gain setting of theAGC is modulated with a proper modulation scheme (e.g. FM, AM, PM, FSK,MSK, ASK, PSK etc.) and transported on a dedicated frequency carrier tothe RU over the copper cable. The gain compensator in the RU receivesthe demodulated information of the gain setting and compensates the gainaccordingly.

Furthermore, according to another embodiment, to suppress glitchesoccurring due to the gain change delay between the AGC and the VGA, asecond local AGC is added in the RU for glitch suppression. The secondlocal AGC also protects the ADC from saturation.

RoCu Link Noise Factor

Noise factor is a key parameter in analog system design. It basicallymeasures how noisy the system is. The noise factor represents the factorby which the output noise level is increased from the input noise level,No, attributable to thermal noise in the input termination at standardnoise temperature TO (usually 290 K). Noise factor in dB is normallyreferred to as noise figure. If there are no other interferences at theinput, the noise figure represents the SNR degradation of the system.For a receiver design, noise factor represents the receive sensitivitydegradation.

FIG. 8 shows a system model for calculating the noise factor of a RoCuUL link. The received UL RF signal, sent from a UE and received by anantenna 801 is first mixed down by an RF/IF unit 802 of the RH to an IFfrequency, preferably a low IF frequency. Then the mixed-down IF signalis transmitted over the copper cable, illustrated as Cat5/6/7 in FIG. 8.The RF/IF unit 802 is modeled with the gain of Ga and the noise factorof Fa. The IF signal goes through the copper cable with cable lossmodeled as Lc. The cable background noise is modeled as an additivenoise source with noise level Nc, which is used to model theElectromagnetic Interference, EMI, noise coupled into the cable from theoutside. Then the IF signal is received by a copper receiver unit, Cu RX803, e.g. of the RU, with the gain of Gb and the noise factor of Fb.Thereafter, the IF signal is converted from analog to digital form in ananalog to digital, ADC, unit 804.

As modeled in FIG. 8, the noise factor of the system can be calculatedas

$F = {F_{a} + {\frac{N_{c}/N_{0}}{G_{a}}L_{c}} + {\frac{F_{b} - 1}{G_{a}}L_{c}}}$

From the equation above, the higher the gain G_(a) is, the lower thenoise factor is. In practice, the first term F_(a) is relatively small.Approximately, the noise factor is proportional to the ratioL_(c)/G_(a). In an example discussed in this disclosure, we assumeF_(a)=3 dB, F_(b)=10 dB, N_(c)=−160 dBm/Hz and N₀=−174 dBm/Hz.

Automatic Gain Control (AGC)

In mobile networks, the range of the received UL signal power is quitelarge due to the varying distance from UEs to the antenna of the basestation. For coordinated UEs under power control, the maximum receivedsignal power can be as high as −40 dBm for near UEs, while the minimumreceived signal power can be below −90 dBm for the far UEs. However,there are possibilities that there are uncoordinated UEs within thesystem bandwidth, which are very close to the antenna and transmit highpower. An uncoordinated UE may be a UE that communicates in a networkdifferent from the present network, that at least partly overlaps withthe present network, but wherein the uncoordinated UE happens to beclose to a base station antenna of the present network. In a severe usecase, when the uncoordinated UE is 1 meter away from the base stationantenna (e.g. 35 dB path loss) and transmits maximum power (e.g. 23dBm), (since the base station it communicates with is far away) themaximum received signal power can be −12 dBm.

Furthermore, due to regulations regarding conducted and/or radiatedemissions, the transmit power over copper cables may be limited to acertain highest allowed value denoted as Pc. For example, for Cat5/6/7cables, for a signal with 20 MHz bandwidth transmitted above 30 MHz, thetransmit power may be limited to a maximum of −3 dBm.

The simplest way for the gain setting is to use a fixed gain. In ordernot to violate the power limit regulation, the maximum fixed gain Gashould be set as

G _(a) =P _(c) −P _(r,max),

where Pc is the regulated transmit power limit of the copper cable andPr,max is the maximum received signal power at an antenna of the RH.When Pr,max is high, Ga will be low and thereby the noise factor ishigh. The higher blocking protection that is required, the higher is thenoise factor, when using a fixed gain setting. This would penalize thereceive sensitivity and the bit rate per coverage.

Using AGC can improve the noise factor, especially when the signal isweak. Ideally, the AGC should dynamically adjust the gain according tothe current received signal power gain as

G _(a)(t)=P _(c) −P _(r)(t)

where Pr(t) is the received signal power at time t. Basically, the gainis adjusted high when the received signal power is low. So the noisefactor can be significantly improved when the signal is weak.

FIG. 9 shows the improvements from using an AGC with 40 dB dynamic rangefor a cable with 20 dB cable loss. For the desired signal power rangefrom −52 to −100 dBm, the noise figure with AGC is 3.1 dB, while thenoise figure without AGC is 26.3 dB. The noise figure is 23 dB improved.It means the receive sensitivity is increased by 23 dB. The maximumcoverage is increased by 5.8 times in radius, assuming path lossexponent=3.1 in air interface. It is worth noting that the gain in thisexample adjusts only for the high received power between −52 dBm and −12dBm. For the desired signal power range, i.e. from −100 dBm to −52 dBm,the AGC setting is constant (49 dB in FIG. 9). Therefore, using AGCenables using high gain for the most relevant range of the users in thecoverage and at the same time using the lower gain to prevent high powerusers to violate the PSD regulation. The AGC can also be used to protectthe copper line driver, mixer etc. from saturation.

In an analog design, the gain adjustment of the AGC may be continuous.The performance has been illustrated by the smooth curve in FIG. 9. In adigital design, the gain adjustment is stepped with several gain values,which can be configured. The steps are indexed (coded in bits), each ofwhich corresponds to a pair of the gain setting for the AGC and the VGAcompensating the AGC gain adjustment. FIG. 10 shows an example of thenoise figure improvement using a 4-level stepped AGC. In this example,only 2 bits are needed to index the steps. This would ease the capacityrequirement for the communication channel for the gain information andmay also simplify the design. In practice, the levels may beconfigurable.

Embodiment of an AGC Design

In the traditional AGC design, the digital, baseband, processing unit(e.g. for PHY layer processing) positioned after an analog to digitalconverter, ADC, in the uplink direction, needs to track the gainadjustment done by the AGC almost simultaneously. It is done by afeedback loop, where the digital processing unit measures the signalstrength and controls the gain of AGC. Or it is done by a feed-forwardloop where the gain adjustment of the AGC is fed to the digitalprocessing unit and the digital processing unit compensates the gainadjustment by AGC before further processing. Without the baseband AGCtracking, it would cause imbalance link budget due to path lossimbalance between DL and UL. This would cause significant performanceissues for some key baseband algorithms (e.g. power control, cellselection, handover etc.), which expect that the DL and UL path lossesor link budget are balanced.

However, the above designs suit only the situation when the AGC iscollocated with the digital processing unit. In the RoCu system, the BBUis located after the ADC in the RU, in the uplink direction, while theAGC is located in the RH. The management channel between RU and RH, usedfor configuration, alarms etc is not fast enough to track the gainadjustment of the AGC since it is designed not to waste valuable IFsignal bandwidth. Low bitrate in combination with, delay caused by theLayer 2, L2, processing (e.g. mux/demux with other messages,en/de-capsulation operations) makes this channel unsuitable for AGCcontrol.

An embodiment of this invention is shown in FIG. 11. On the RH 21 side,the AGC 1101 adjusts the gain setting according to the signal powermeasured at an input of the AGC such that the output power to the coppercable becomes the maximum power allowed or almost the maximum powerallowed over the copper cable. Note that the AGC loop structure, as in astandard AGC circuit (i.e. the loop of power measurement and gainadjustment) is not shown here. The gain setting may also be called theamplification level. The gain setting information, a.k.a. theinformation of the amplification level, e.g. in the format of the analogsignal for analog AGC or in the format of digital signal or bits fordigital AGC, may be modulated in a modulator 1102 with a propermodulation scheme (e.g. frequency Modulated, FM, Phase Modulated, PM,and Amplitude Modulated, AM, for analog signal and Frequency ShiftKeying, FSK, Phase Shift Keying, PSK, and Amplitude Shift Keying, ASK,for digital signal). Further, the modulated signal may be transmitted ona carrier frequency out of band of the RoCu signal band and a managementchannel band. On the RU 10 side, the modulated signal for the AGC gainsetting information is first extracted from the line by proper filteringand demodulated by a demodulator 1105. Then, the demodulated signal(i.e. the gain information) is used to control the gain of a variablegain amplifier, VGA 1106, such that the VGA gain compensates for a gainadjustment done by the AGC 1101. For example, if the AGC reduces itsgain by 5 dB because its input signal gets 5 dB stronger, the VGA shouldincrease its gain by 5 dB to compensate the AGC gain change. In thisway, from the perspective of the digital processing unit, the signalpower is transparent from the antenna to the input of an ADC 1108 of theRU 10. Another advantage is that the invention does not require anychange in the baseband processing software.

In FIG. 11, there are two optional coding blocks: an encoder block 1103after the AGC and a decoder block 1107 before the VGA. Fordigital/stepped AGC, coding the gain data can add redundancy andtherefore increase the robustness of the data. Note that in FIG. 11, thecomponents related to down-conversion (i.e. mixers) are not shown hereto simplify the denotation. For example, in the RH in UL, the receivedRF signal is down-converted to IF signal, and in the RU in UL, the IFsignal is down-converted to a baseband signal.

Delay Compensation for the Communication Channel Extra Delay

The communication channel for communication of the AGC gain settinginformation may experience delay due to e.g. processing delays forencoding/decoding, modulation/demodulation, etc. The same amount ofdelay is not experienced for the actual (data) signal communicated overthe copper cable. As a result, there is a delay between the AGC gainchange and the gain compensation in the VGA. This delay would causeglitches in the signal (sudden changes in signal amplitude). Theglitches modulate the signal in amplitude and cause distortions to thedesired signal. This can significantly degrade the performance, i.e. thequality of the transmitted signal. To minimize the delay for thetransmission of the AGC setting information in relation to thetransmission of the signal, a delay circuit is inserted to delay thesignal such that the signal adjusted by the AGC arrives at the VGA atthe same time as the VGA changes its gain to compensate the AGC. As oneexample, shown in FIG. 12, a delay circuit 1104 is inserted after theAGC block 1101 in the embodiment of FIG. 11. It can also be placed inother places in FIG. 11 to balance the delay. For example, the delaycircuit can be placed also in front of the VGA in the RU. If thetransmission delay of the communication channel for processing andtransmitting the AGC gain setting information in relation to the signaltransmission delay is known, the delay circuit is configured to delaythe signal by the known delay difference. This may be necessary if thecommunication channel delay is not sufficiently low.

2nd AGC in RU for Glitch Suppression

With the delay circuit 1104, the distortions due to glitches are loweredbut it is difficult to completely remove the glitches. For example, itis difficult to exactly estimate the extra delay of the gain settingcommunication channel delay. In FIG. 13, a 2nd AGC 1200, comprising aVGA, an ADC and a digital signal processor, DSP, is added after theVGA1106 in the RU10 to suppress the remaining glitches. Basically, theDSP detects samples affected by the glitches and then mitigates theglitch effect by zeroing-out the samples or reducing the amplitude ofthe samples. It has been proven an effective method to mitigate shortglitches, especially in presence of strong blocking signals. Moredetails can be found in patent application document WO 2011/075024. Afurther advantage with the 2nd AGC is that it protects the signal fromsaturating the ADC.

Distributed Antenna System, DAS, Configuration

A DAS configuration equipped with the invented AGC system is illustratedin FIG. 14. The signals received from a first branch (upper branch infigure) and from the second branch (lower branch in figure) are combinedtogether before reaching the second AGC 1200. The FIG. 14 only shows twobranches but is equally applicable for a multiple of branches, or allbranches. By having only one ADC for a plurality of branches, e.g. allbranches, reduces the hardware costs.

In a DAS configuration, the signals from different RH branches arecombined together in a signal combiner before going through the ADC ofthe second AGC 1200. In this case, the noise figure for any branch k is

$F_{{DAS},k} = {F_{k} + {\left( \frac{1}{G_{k}} \right){\sum\limits_{i \neq k}{G_{i}F_{i}}}}}$

where Fi is the noise factor per branch and Gi is the overall gain fromantenna to the signal combiner including the gains of IF/RF and Cu Rx(Ga and Gb), and the cable loss (Lc). It shows that the noise figure isincreased by the second term due to the signal combining.

When severe blocking happens in one branch, its noise figure couldincrease dramatically. Due to the signal combining, the noise figureincrease in the blocking branch increases the noise figure in otherbranches as well. Reducing the gain of the blocking branch can reducethe noise figure of other (non-blocked) branches at the cost of furtherreduced performance in the blocked branch. A blocking signal above acertain level thus represents a special operating condition where it maybe beneficial for the system to deviate from the transparent gainapproach used in normal operating conditions. This can be represented indifferent ways, e.g. by a threshold on input power or on the amount ofgain compensation.

When a branch is blocked above the special operating conditionthreshold, the gain adjustment of the VGA in the first AGC can switch topartial instead of full compensation of the gain change of the AGC. Thiswill reduce the overall noise figure due to the reduced total gain forthe blocked branch. The UEs connected to other branches (RH ports) wouldbenefit from the reduced noise figure. Examples of partial compensationinclude fractional dB compensation (e.g. 0.5 dB compensation for everydB AGC change above the special operating condition threshold), zerocompensation above the special operating condition threshold, or evennegative compensation (suppressing the signal further, including thepossibility to completely disable the branch).

When cable noise is high e.g. due to crosstalk, more levels of gain areneeded. It also needs a bigger dynamic range to have a higher gain toreduce the noise figure for weak signals. FIG. 15 shows such needs withan example of high cable noise of −130 dBm/Hz.

Regarding the gain information communication channel, the gaininformation can be modulated in different forms, e.g. in amplitude,phase, frequency etc. Different gain levels can also be coded by theon-off states of several frequency carriers.

The gain information may also be information of the gain adjustment ofthe AGC in the RH, i.e. the change of gain or amplification. This cansimplify the communication channel design. For example, the gaininformation can be coded with 2 bits, in which 00 means invalid, 01means gain increased, 10 means gain decreased and 11 means unchanged. Asan example, this can be easily coded with two tones. 00 is tone 1 offand tone 2 off, 01 is tone 1 off and tone 2 on, 10 is tone 1 on and tone2 off, and 11 is tone 1 on and tone 2 on. The RH has a gain table andthe RU has a gain compensation table, which are 1-to-1 matched. The RHadjusts the gain one step up or down only at a time according to thegain table. The RU detects the on-off states of two tones and adjustsaccordingly the gain compensation one step up or down according to thegain compensation table. In this way, the gain change in the RH and thegain compensation in the RU are synchronized. Basically, for the RU tocompensate on a large change in amplification/gain at the RH side, itmay take multiple steps.

FIG. 16 shows a part of a base station system of a wirelesscommunication network, the base station system comprising a basebandunit, BBU, a radio unit, RU 10 and a radio head, RH, 21. The RU 10 isconnected to the RH 21 via a metallic conductor 40. The BBU is connectedto the RU 10. The base station system is arranged for increasing signalquality of signals sent from the RH to the RU over the metallicconductor. The RH 21 comprises an amplifying unit 1602 for amplifying asignal to be transmitted from the RH to the RU and for changing itsamplification level, and a transmitting unit 1604 for transmitting theamplified signal to the RU. The RU 10 comprises a receiving unit 1611for receiving the amplified signal, and a compensating unit 1612 capableof adapting its amplification level, for compensating for the change insignal amplification level performed at the RH such that the strength ofthe signal is transparent to the base station system.

According to an embodiment, the transmitting unit 1604 of the RH may bearranged for transmitting information of a current signal amplificationlevel at the RH to the RU. The receiving unit 1611 of the RU may bearranged for receiving information of the current amplification level atthe RH and the compensating unit 1612 of the RU may be arranged forcompensating for the change in signal amplification level performed atthe RH according to the received information.

Further, the base station system in FIG. 16 may comprise a plurality ofRHs 21-22, arranged as the RH of FIG. 16 and a plurality of the RUs10-11 arranged as the RUs of FIG. 16. In addition, the base stationsystem may comprise a combiner (1400 in FIG. 14) for combining an outputsignal from each of the compensating units 1612 of the plurality of RUs,and an automatic gain control, AGC, unit (1200 in FIG. 14) connected tothe combiner for receiving the combined output signals.

In FIG. 17 an RH 21 according to an embodiment is shown, which isoperable in a base station system of a wireless communication network,for increasing signal quality of signals transmitted from the RH to anRU, over a metallic conductor. The base station system comprises a BBU,the RU and the RH. The RH is connected to the RU via the metallicconductor. The RH 21 comprises an amplifying unit 1602 for amplifying asignal to be transmitted from the RH to the RU and for changing theamplification level, and a transmitting unit 1604 for transmitting theamplified signal to the RU for subsequent compensation for the signalamplification level change at the RH such that the strength of thesignal is transparent to the base station system. The amplifying unitmay be an automatic gain control, AGC, unit or any other similar unitthat may adapt the amplification level such that the unit outputs arequested signal output level, and possibly also outputs information ofthe amplification level. The RH 21 110 may further comprise acommunication unit 1606, which may be considered to compriseconventional means for communication from and/or to the ‘RU and fromand/or to mobile stations. The network node 110 may further comprise oneor more storage units or memories 1607.

According to an embodiment, the amplifying unit 1602 is arranged toamplify the signal to be transmitted to a signal strength levelapproximately equal to a maximum allowed signal strength level of themetallic conductor, or to amplify the signal to be transmitted with amaximum possible gain of the amplifier, when the signal strength levelto which the signal is amplified with maximum possible gain is below themaximum allowed signal strength level of the metallic conductor. I.e.when the signal level inputted to the amplifying unit is of suchamplitude that when it is amplified with maximum gain of the amplifyingunit, the output signal strength level is below the maximum allowedsignal strength level of the metallic conductor, the signal is to beamplified with maximum gain. If this is not the case, i.e. when theoutput signal strength level would be above the maximally allowed ifamplified with maximum gain, the signal is amplified with a gain thatmakes the output signal be similar to the maximum allowed signalstrength level or advantageously a slight bit below the maximum allowedsignal strength level.

According to another embodiment, the transmitting unit 1604 may furtherbe arranged for transmitting information of a current signalamplification level to the RU.

According to another embodiment, the transmitting unit 1604 may furtherbe arranged for transmitting the information of the signal amplificationlevel over a carrier frequency outside a frequency band used for thetransmission of the amplified signal.

According to another embodiment, the RH may further comprise a delaycircuit 1603 for delaying the transmission of the signal in relation tothe transmission of the information of the current amplification levelsuch that the signal is received at the RU at substantially the sametime as a compensation is started to be performed at the RH according tothe transmitted information of the current amplification level. Thedelay circuit may alternatively be placed in the RU, before the signalreaches the compensating unit. The RH may further comprise a receivingunit 1601 for receiving the incoming signal from mobile stationscommunicating with the RH via the antenna 50 of the RH.

The receiving unit 1601, the amplifying unit 1602, the delay unit 1603and the transmitting unit 1604 may be arranged in an arrangement 1605.The arrangement 1605 could be implemented e.g. by one or more of: aprocessor or a micro processor and adequate software and storagetherefore, a Programmable Logic Device, PLD, or other electroniccomponent(s)/processing circuit(s) configured to perform the actions, ormethods, mentioned above.

FIG. 18 schematically shows an embodiment of an arrangement 1800 for usein an RH 21, which also can be an alternative way of disclosing anembodiment of the arrangement 1605 in an RH 21 illustrated in FIG. 17.Comprised in the arrangement 1800 is a processing unit 1806, e.g. with aDigital Signal Processor (DSP), micro processor etc. The processing unit1806 may be a single unit or a plurality of units to perform differentactions of procedures described herein. The arrangement 1800 may alsocomprise an input unit 1802 for receiving signals from other entities,and an output unit 1804 for providing signal(s) to other entities. Theinput unit 1802 and the output unit 1804 may be arranged as anintegrated entity.

Furthermore, the arrangement 1800 comprises at least one computerprogram product 1808 in the form of a non-volatile or volatile memory,e.g. an Electrically Erasable Programmable Read-only Memory (EEPROM), aflash memory, a disk drive or a Random-access memory (RAM). The computerprogram product 1808 comprises a computer program 1810, which comprisescode means, which when executed in the processing unit 1806 in thearrangement 1800 causes the arrangement 1605 and/or the RH 21 to performthe actions of any of the procedures described earlier in conjunctionwith FIGS. 4-5.

The computer program 1810 may be configured as a computer program codestructured in computer program modules. Hence, in an exemplifyingembodiment, the code means in the computer program 1810 of thearrangement 2000 comprises an amplifying module 1810 a for amplifying,by an amplification unit, a signal to be transmitted from the RH to theRU. The code means further comprises a changing module 1810 b forchanging the signal amplification level. The code means furthercomprises a transmitting module 1810 c for transmitting the amplifiedsignal to the RU for subsequent compensation for the signalamplification level change at the RH such that the strength of thesignal is transparent to the base station system. The code means mayfurther comprise a second transmitting module 1810 d for transmittinginformation of a current signal amplification level to the RU.

In FIG. 19 an RU 10 is shown, which is operable in a base station systemof a wireless communication network and arranged for increasing signalquality of signals sent from an radio head, RH 21, to the RU over ametallic conductor. The base station system comprises a BBU, the RU andthe RH. The RU is connected to the RH via the metallic conductor. The RU10 comprises a receiving unit 1611 for receiving a signal transmittedfrom the RH, the signal being amplified at the RH. The RU furthercomprises a compensating unit 1612 capable of adapting its amplificationlevel for compensating for the signal amplification performed at the RHsuch that the strength of the signal is transparent to the base stationsystem. The RU 10 may further comprise a communication unit 1616, whichmay be considered to comprise conventional means for communication fromand/or to the RH and from and/or to the BBU. The network node 110 mayfurther comprise one or more storage units or memories 1617.

According to an embodiment, the receiving unit 1611 may further bearranged for receiving information of a current amplification level atthe RH from the RH. The compensating unit 1612 may further be arrangedfor compensating according to the received information.

According to an embodiment, the receiving unit 1611 may be arranged forreceiving of information of a current amplification level by, at a firstpoint of time, receiving information from the RH of a currentamplification level at the RH, and at a second point of time later thanthe first point of time, receiving information from the RH of a currentamplification level at the RH. The compensating unit 1612 may bearranged for comparing the amplification level at the second point oftime with the amplification level at the first point of time to detect adifference in amplification level, and for compensating according to thedetected difference in amplification level.

According to another embodiment, the receiving unit 1611 is arranged forreceiving the information of the current amplification level over acarrier frequency outside a frequency band used for the reception of thesignal.

According to another embodiment, the RU may further comprise a glitchadjustment unit 1613 arranged after the compensating unit 1612 in apropagation direction of the received signal, for detecting suddenchanges in signal strength, and for adjusting the detected changes suchthat the strength of the signal is reduced at the detected changes. Theglitch adjustment unit may be a fast AGC, which may also be used toprotect the ADC from saturation.

According to another embodiment, the compensating unit 1612 is arrangedfor compensating for a signal amplification adjustment performed at theRH only if under normal operating conditions, and, if under a specialoperating condition differing from the normal operating conditions, thecompensating unit is arranged for only partially compensating for thesignal amplification adjustment performed at the RH. The compensatingunit may be a variable gain amplifier or any other similar unit (e.g. avariable attenuator) that can adapt its gain amplification such that ifthe signal amplification at the RH is increased with an amount, thesignal amplification at the compensating unit is decreased with the sameamount. For this reason the variable gain amplifier or any other similarunit may also be arranged with an information receiving input forreceiving information of the current amplification level at the RH andadapt its gain amplification according to the received information.

The RU 10 may further comprise a transmitting unit 1614 for transmittingthe compensated signal to the BBU. The receiving unit 1611, thecompensating unit 1612, the glitch adjustment unit 1613 and thetransmitting unit 1614 may be arranged in an arrangement 1615. Thearrangement 1615 could be implemented e.g. by one or more of: aprocessor or a micro processor and adequate software and storagetherefore, a Programmable Logic Device, PLD, or other electroniccomponent(s)/processing circuit(s) configured to perform the actions, ormethods, mentioned above.

FIG. 20 schematically shows an embodiment of an arrangement 2000 for usein an RU 10, which also can be an alternative way of disclosing anembodiment of the arrangement 1615 in an RU 10 illustrated in FIG. 19.Comprised in the arrangement 2000 is a processing unit 2006, e.g. with aDigital Signal Processor (DSP). The processing unit 2006 may be a singleunit or a plurality of units to perform different actions of proceduresdescribed herein. The arrangement 2000 may also comprise an input unit2002 for receiving signals from other entities, and an output unit 2004for providing signal(s) to other entities. The input unit 2002 and theoutput unit 2004 may be arranged as an integrated entity.

Furthermore, the arrangement 2000 comprises at least one computerprogram product 2008 in the form of a non-volatile or volatile memory,e.g. an Electrically Erasable Programmable Read-only Memory (EEPROM), aflash memory, a disk drive or a Random-access memory (RAM). The computerprogram product 2008 comprises a computer program 2010, which comprisescode means, which when executed in the processing unit 2006 in thearrangement 2000 causes the arrangement 1615 and/or the RU 10 to performthe actions of any of the procedures described earlier in conjunctionwith FIGS. 6-7.

The computer program 2010 may be configured as a computer program codestructured in computer program modules. Hence, in an exemplifyingembodiment, the code means in the computer program 2010 of thearrangement 2000 comprises a receiving module 2010 a for receiving asignal transmitted from the RH, the signal being amplified by anamplification unit at the RH. The code means further comprises acompensating module 2010 b for compensating, by a compensating unitcapable of adapting its amplification level, at the RU, for a signalamplification change performed at the RH such that the strength of thesignal is transparent to the base station system. The code means mayfurther comprise a second receiving module 2010 c for receivinginformation of a current signal amplification level to the RU, and acontrol module 2010 d for controlling the compensating of thecompensating module according to the received information.

The acts which have above been described as being implemented orexecuted by a processor may be performed by any suitable machine. Themachine may take the form of electronic circuitry in the form of acomputer implementation platform or a hardware circuit platform. Acomputer implementation of the machine platform may be realized by orimplemented as one or more computer processors or controllers as thoseterms are herein expansively defined, and which may execute instructionsstored on non-transient computer-readable storage media. In such acomputer implementation the machine platform may comprise, in additionto a processor(s), a memory section, which in turn can comprise randomaccess memory; read only memory; an application memory, a non-transitorycomputer readable medium which stores, e.g., coded non instructionswhich can be executed by the processor to perform acts described herein;and any other memory such as cache memory, for example. Another exampleplatform suitable is that of a hardware circuit, e.g., an applicationspecific integrated circuit, ASIC, wherein circuit elements arestructured and operated to perform the various acts described herein.

The invention according to any of the described embodiments has one ormore of the following advantages: Reducing system noise figuresignificantly; Increase copper cable reach; Mitigate blocking scenario;Increase radio coverage; Increase UE battery time.

A radio head is equivalent to an active antenna element, a radio unit isequivalent to a radio resource unit and a baseband unit is equivalent toa digital unit.

The metallic conductor between the RH and the RU may in some cases bereplaced by a microwave link, a milliwave link, or similar type of link,and at least some of the methods may be useable also in such a system.

Although the description above contains a plurality of specificities,these should not be construed as limiting the scope of the conceptdescribed herein but as merely providing illustrations of someexemplifying embodiments of the described concept. It will beappreciated that the scope of the presently described concept fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the presently described concept isaccordingly not to be limited. Reference to an element in the singularis not intended to mean “one and only one” unless explicitly so stated,but rather “one or more.” All structural and functional equivalents tothe elements of the above-described embodiments that are known to thoseof ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed hereby. Moreover, it is notnecessary for an apparatus or method to address each and every problemsought to be solved by the presently described concept, for it to beencompassed hereby.

1. A method performed by a base station system of a wirelesscommunication network, the base station system comprising a basebandunit (BBU), a radio unit (RU), and a radio head (RH), wherein the RU isconnected to the RH via a metallic conductor, the method comprising, atthe RH: amplifying a signal to be transmitted from the RH to the RU;changing a signal amplification level; and transmitting the amplifiedsignal to the RU, the method further comprising, at the RU: receivingthe amplified signal; and compensating for the change in signalamplification level performed at the RH.
 2. The method according toclaim 1, wherein the signal to be transmitted is amplified to a signalstrength level approximately equal to a maximum allowed signal strengthlevel of the metallic conductor, or is amplified by a maximum possiblegain of the amplifier, when the signal strength level to which thesignal is amplified with maximum possible gain is below the maximumallowed signal strength level of the metallic conductor.
 3. The methodaccording to claim 1, further comprising transmitting information of acurrent signal amplification level at the RH to the RU.
 4. The methodaccording to claim 1, further comprising: receiving, at the RU,information of a current amplification level at the RU from the RH; andcontrolling the compensating according to the received information. 5.The method according to claim 4, wherein the receiving of informationcomprises, at a first point of time, receiving information from the RHof a current amplification level at the RH and at a second point of timelater than the first point of time, receiving information from the RH ofa current amplification level at the RH, and comparing the amplificationlevel at the second point of time with the amplification level at thefirst point of time to detect a difference in amplification level, andwherein the compensating is controlled according to the detecteddifference in amplification level.
 6. The method according to claim 4,wherein the information of the current amplification level is receivedover a carrier frequency outside a frequency band used for the receptionof the signal.
 7. The method according to claim 1, further comprising,after the compensating has been performed, detecting sudden changes insignal strength, and adjusting the detected changes such that the signalstrength is reduced at the detected changes.
 8. The method according toclaim 1, wherein the compensating for the signal amplification changeperformed at the RH is only performed if under normal operatingconditions, and, if under a special operating condition differing fromthe normal operating conditions, the compensating for the signalamplification change performed at the RH is only partially performed. 9.The method according to claim 8, further comprising, after thecompensating has been performed, detecting sudden changes in signalstrength, and adjusting the detected changes such that the signalstrength is reduced at the detected changes.
 10. A base station systemof a wireless communication network, the base station system comprisinga baseband unit (BBU), a radio unit (RU), and a radio head (RH), the RUbeing connected to the RH via a metallic conductor, the BBU beingconnected to the RU, wherein the RH comprises: an amplifying unit toamplify a signal to be transmitted from the RH to the RU and to changeits amplification level; and a transmitting unit to transmit theamplified signal to the RU, and the RU comprises: a receiving unit toreceive the amplified signal; and a compensating unit to adapt itsamplification level to compensate for the change in signal amplificationlevel performed at the RH.
 11. The base station system according toclaim 10, comprising a plurality of the RHs and a plurality of the RUs,and further comprising a combiner to combine an output signal from eachof the compensating units of the plurality of RUs, and an automatic gaincontrol (AGC) unit connected to the combiner to receive the combinedoutput signals.
 12. The base station system according to claim 10,wherein the amplifying unit amplifies the signal to be transmitted to asignal strength level approximately equal to a maximum allowed signalstrength level of the metallic conductor, or amplifies the signal to betransmitted by a maximum possible gain of the amplifier, when the signalstrength level to which the signal is amplified with maximum possiblegain is below the maximum allowed signal strength level of the metallicconductor.
 13. The base station system according to claim 10, whereinthe transmitting unit further transmits information of a current signalamplification level at the RH to the RU.
 14. The base station systemaccording to claim 10, wherein the receiving unit further receivesinformation of a current amplification level at the RH from the RH, andthe compensating unit compensates for the change in signal amplificationlevel performed at the RH according to the received information.
 15. Thebase station system according to claim 10, wherein the receiving unitreceives information of a current amplification level by, at a firstpoint of time, receiving information from the RH of a currentamplification level at the RH, and at a second point of time later thanthe first point of time, receives information from the RH of a currentamplification level at the RH, and the compensating unit compares theamplification level at the second point of time with the amplificationlevel at the first point of time to detect a difference in amplificationlevel, and compensates according to the detected difference inamplification level.
 16. The base station system according to claim 14,wherein the receiving unit receives the information of the currentamplification level over a carrier frequency outside a frequency bandused for the reception of the signal.
 17. The base station systemaccording to claim 10, further comprising a glitch adjustment unitarranged after the compensating unit in a propagation direction of thesignal, to detect sudden changes in signal strength, and to adjust thedetected changes such that the strength of the signal is reduced at thedetected changes.
 18. The base station system according to claim 13,wherein the compensating unit compensates for a signal amplificationadjustment performed at the RH only if under normal operatingconditions, and, if under a special operating condition differing fromthe normal operating conditions, the compensating unit only partiallycompensates for the signal amplification adjustment performed at the RH.19. A non-transient computer-readable storage medium that storesinstructions, which when run in a radio head (RH) operable in a basestation system of a wireless communication network, wherein the basestation system comprises a baseband unit (BBU), a radio unit (RU), andthe RH, the RH being connected to the RU via a metallic conductor, theinstructions causing the RH to perform the following operations:amplifying a signal to be transmitted from the RH to the RU; changing asignal amplification level; and transmitting the amplified signal to theRU for subsequent compensation for the signal amplification level changeat the RH.
 20. The non-transient computer-readable storage mediumaccording to claim 19, the instructions further causing: receivinginformation of a current amplification level at the RU from the RH; andcontrolling the compensating according to the received information.